Nearly one in seven people in the United States suffer from some type of chronic sleep disorder, and only 50% of people are estimated to get the recommended seven to eight hours of sleep each night. It is further estimated that sleep deprivation and its associated medical and social costs (loss of productivity, industrial accidents, etc.) exceed $150 billion per year. Excessive sleepiness can deteriorate the quality of life and is a major cause of morbidity and mortality due to its role in industrial and transportation accidents. Sleepiness further has undesirable effects on motor vehicle driving, employment, higher earning and job promotion opportunities, education, recreation, and personal life.
Primary sleep disorders affect approximately 50 million Americans of all ages and include narcolepsy, restless legs/periodic leg movement, insomnia, and most commonly, obstructive sleep apnea (OSA). OSA's prevalence in society is comparable with diabetes, asthma, and the lifetime risk of colon cancer. OSA is grossly under diagnosed; an estimated 80-90% of persons afflicted have not received a clinical diagnosis. Some medical conditions have been associated with increased risk for sleep disorders, specifically sleep-related breathing disorders. Such conditions include cardiovascular disease such as hypertension, stroke, and congestive heart failure. Evidence indicates that treatment of the sleep-related breathing disorder can improve cardiac function in these patients. Similarly, evidence indicates sleep-related breathing disorders can increase the prevalence of nocturnal cardiac arrhythmia development.
Sleeping disorders are currently diagnosed by two general methods. Subjective methods, such as the Epworth and Standford Sleepiness Scale, generally involve questionnaires that require patients to answer a series of qualitative questions regarding their sleepiness during the day. With these subjective methods, however, it is found that the patients usually underestimate their level of sleepiness or they deliberately falsify their responses because of their concern regarding punitive action or as an effort to obtain restricted stimulant medication. The second group of methods uses physiological evaluations, such as all-night polysomnography to evaluate a patient's sleep architecture (e.g., obtaining respiratory disturbance index to diagnose sleep apnea). A polysomnogram (PSG) can also be followed by an all-day test such as the Multiple Sleep Latency Test (MSLT) or its modified version, the Maintenance of Wakefulness Test (MWT). The PSG typically requires patients to spend the night in a sleep laboratory connected to multiple sensors while they attempt to sleep.
Sleep laboratory studies require the patient to physically go to the sleep lab to be tested. These labs typically have a small number of sleeping rooms containing all the necessary sleep study equipment. The equipment from each room many times is wired to a central monitoring room where a sleep technician collects and analyzes data from several subjects. Due to the limited capacity and a high volume of patients requiring sleep studies, many labs have unacceptable waiting lists. Additionally, many patients requiring sleep studies have related medical conditions, such as severe cardiovascular disease, or are immobile making travel to a sleep lab difficult. As a result, many patients must wait for an available appointment or improved health before a laboratory-based sleep study is possible. This delay in diagnosing the patient's sleep disorder leads to a delay in treatment and an increased risk of developing a related medical condition.
Current methods attempting to conduct a sleep study at the patient's location have proved unsuccessful. Patients who are already ill or hospitalized cannot travel to a sleep lab, nor can a sleep test be conducted in an inpatient hospital room. Standard, and even specialized, hospital rooms are not equipped to conduct a sleep study. Facilities are not frequently retrofitted with sleep study equipment due to the huge expense involved, particularly for limited use. Further, hospital rooms are crowded with other equipment, which makes adding bulky sleep study carts infeasible. Similarly, few hospitals have space near patient rooms available for use as a monitoring room.
To address some of these concerns, methods have been developed to conduct unattended studies. An unattended sleep test does not require the step of transmitting the data to a monitoring location. These methods have relied on equipment incapable of transmitting data during the sleep study, creating the unattended test. Such unattended tests, however, are plagued with signal failure. In one study involving unattended PSG, data from over 23% of the patients were unusable due to missing channels, even though a technician called the PSG recording device every 30 minutes to check the quality of the recordings. Further, unattended tests do not resolve the problem of fitting a sleep cart into a crowded patient room.
None of the current methods for conducting a sleep study outside a sleep lab allow transmission of the collected data during the test. All of the current methods require the PSG data to be stored during the test and read only after the test has been completed. As such, the data cannot be periodically or continuously checked for adequacy. Even if the data were periodically evaluated, the current methods do not use a step of allowing a remote monitor to communicate with the subject to correct any sensor/signal problems. The current methods also do not include live video feeds that enable a remote monitor to visualize the subject during the sleep test. Moreover, the current methods make it extremely difficult to conduct a full polysonnagram sleep study outside a sleep lab have enabled the entire sleep system to fit inside a crowded hospital room.
It is therefore an object of the present invention to provide a method of conducting a sleep analysis outside a sleep lab wherein the data is transmitted at substantially the same time it that is collected or created. It is another object of the present invention to provide a method of conducting a sleep analysis outside the sleep lab that is remotely attended. It is another objective of the present invention to provide a method of conducting a sleep analysis outside the sleep lab on subjects who are already patients in a hospital room. It is still another objective of the present invention to provide a method of conducting a sleep analysis with a small, lightweight data acquisition system.